I removed it because it wasn't updating live, and I've put in place REPLICA_SET_ENDPOINTS so you can see all nodes.  Happy to see secondaries emerge but I would suggest:

* for each of them we have both an "entity" variant and a "hostname" (or "hostAndPort") variant
* we make sure they update live

and we should do this for other roles (nonvoting etc) too as we add them.

should be easy enough to add as many as we want to the existing subscriptions set up in `ReplicaSetImpl.start`.  (but we may need allMembers SERVICE_UP also triggering updates!)